In the manufacture of paper and paperboard intended for some kind of printing the print-receiving surface is treated either by a pure starch solution or by a coating slip. When traditional starch of any known origin (potato, maize, wheat and tapioca) is used, more than one chemical modification step is required in many cases to obtain a product possessing sufficient stability. The various modification steps usually include a stabilising step, for instance an etherification reaction with propene dioxide or an esterification reaction with vinyl acetate or acetic anhydride, and a degradation step, such as oxidation, enzymatic degradation, acid hydrolysis or so-called thermo-chemical conversion. During the above steps substitution of the starch takes place, and the degree of substitution pertaining to the corresponding stabilising step usually amounts to 0.01-0.5 mole/mole glucose, preferably 0.05-0.20 mole/mole.
The necessity to carry out more than one modification step entails costs and has negative effects on the environment, and a reduction of the required number of chemical modification steps thus is desirable.